The present invention relates a sound absorber for blowers.
In blowers there is an especially extensive noise generation, when high flow speeds and a great pressure increase is produced at high rotary speeds. It can be reduced by sound absorbers, which are arranged in the aspiration region.
In stroke piston internal combustion engines carbon monoxide and hydrocarbon compounds are produced in the exhaust gas during a cold start because of the incomplete combustion resulting from the mixture expansion. If fresh air is blown into an exhaust system of a stroke piston internal combustion engine, an exothermic post-oxidation of the hydrocarbon compounds is produced. The contents of the carbon monoxide and hydrocarbon compounds is thereby directly reduced. Additional heat is supplied to the catalysts by the combustion process, which is advantageous for the cold start. The catalysts reaches fast a favorable operational temperature.
During blowing of fresh air into the exhaust system secondary blowers are utilized. The fresh air can be aspirated through an air filter of the stroke piston internal combustion engine. Additional conduits are provided for this purpose and involve substantial expenses. If the fresh air is aspirated from the free atmosphere, for example through a not closed opening, the noise generation from the blower which is produced for the above mentioned reasons must be absorbed or dampened. For this purpose separate sound absorbers are used for the blower.
Such a blower is disclosed for example in the German patent document DE A1 4205489 and shown in this reference in FIGS. 5 and 6. The sound absorber has a housing cup with a flat cup bottom, a cup wall and a housing cover which closes the cup opening. An air inlet opening is formed by a bore hole in the cup wall, and an air outlet passage is formed by a central bore hole. The air inlet opening and the air outlet passage are connected by a spiral passage. The passage is formed by a damping insert of an open-pore, sound absorbing material. The passage from the cup bottom to the housing cover extends in an axial direction of the blower. The passage is limited by the cup bottom and the housing cover.
The noise generation, especially an aspiration noise produced in the region of the aspiration opening of the blower and thereby at the air outlet passage of the sound absorber is not sufficiently dampened.